The present invention relates to a process for fastening a miniaturized component, in particular assembled in a modular manner, on a baseplate by a solder joint.
DE-A-195 33 426 describes a mechanical fastening system for microoptical elements, assembled in a modular manner, preferably in a housing, on a baseplate for the production of an optical or optoelectronic layout. A holder is formed with a central platform which carries the single module. At least three legs which are fastened to the baseplate, for example by laser spot welding or soldering, are linked to the platform, preferably via hinges. This known fastening system makes it possible to keep optical components stable to shock and vibration in a wide temperature range.
The prior art discloses the performance of microsoldering using laser beams, the two parts to be joined touching one another, cf. J. L. Jellison et al.: xe2x80x9cMicrosoldering and microminiature welding with lasersxe2x80x9d, Microjoining, September 1988, pages 99-107. The testing of solder joints of those connecting surfaces of two components which have been pressed against one another during soldering, at high packing density, is an important problem. For the production of the solder joint, solder beads are produced on the connecting surfaces of a chip component and on the coordinated connecting surfaces of, for example, a substrate or a baseplate. The respective connecting surfaces are brought into contact and heated until the solder material melts, cf. P. A. Burdett et al.: Inspection technique for flip chip bonded devicesxe2x80x9d, Microjoining September 1988, pages 39-45 and 47-50. To round off the prior art, reference is made to Stockham, Microjoining, September 1988, page 27, FIGS. 1 and 2.
It is the object of the present invention to provide a process for joining two parts by soldering which permits extremely accurate positioning.
This object is achieved, according to the invention, by the features of claim 1.
Advantageous developments of the subject of the invention are evident from the subclaims.
The process according to the invention advantageously permits soldering flux-free and accurate solder connection of, in particular, optical, optoelectronic, electronic and miniaturized, mechanical components on a baseplate along six degrees of freedom. In particular, the process according to the invention can advantageously be carried out in a simple manner.
The energy used in the soldering process according to the invention is supplied by energy flows of different types, such as a laser beam, UV irradiation or a magnetic field which is generated by an inductance of high frequency. In all cases, the energy flow passes through the baseplate in order to melt the thin layer of solder material.
Without imposing any restriction, the manner in which the novel soldering process permits optical elements to be fastened on a baseplate with the use of a laser beam is described here. The optical elements are fastened inside a housing whose side to be connectedxe2x80x94referred to below as the basexe2x80x94is coated with a solder material, such as tin solder or a tin alloy solder. The baseplate must have good light transmittance within the wavelength range of the laser beams used. That surface of the baseplate which faces the housing is preferablyxe2x80x94at least partlyxe2x80x94coated with a grid-like metal pattern. The housing to be fastened is held a suitable distance, for example a few tenths of a millimetre, above the baseplate without mechanical contact with the baseplate. If the laser beam is directed upward from below toward the surface of the baseplate, a fraction of its energy heats the metal pattern while the remainder passes through the free areas of the pattern, reaches the base of the housing and causes the solder material present on the base to melt, with the result that a drop of solder material is formed. The drop fills the space between the baseplate and the base of the housing, with the result that a strong and good solder joint is produced after solidification.